The present invention pertains generally to automated materials applications systems and, more particularly, to automated systems adapted for application of hot melt materials which must be heated to high temperatures in order to flow through applications equipment.
Automated material applications systems for hot melt materials typically have a pump which draws material from a reservoir, and directs it through a heated manifold to one or more application devices such as spray guns. The spray guns are controlled or triggered to apply the material to a substrate at a desired rate and pattern. In the case of hot melt materials, i.e., materials which are fluid only at relatively high temperatures, the material must be heated continuously throughout the system in order to insure adequate flow and application. This may be done by heating the material within the reservoir, heating the reservoir directly, using a heated manifold which is connected to the reservoir to preheat the material before it is pumped through a heated line, and attaching a secondary manifold to the gun application device.
In such systems it is helpful to be able to closely monitor and regulate temperature and pressure of the material. In more complex systems with large or multiple reservoirs, and with multiple application devices and separate lines leading to the application devices, monitoring and regulating material temperature and pressure and application rate is more problematic. Non-uniformities in material temperature and pressures throughout the system can produce flaws in the applied coatings. For example, in systems which employ piston pumps to pump material from a reservoir and through a manifold to an applicator such as a spray gun, pressure spikes are created during the power or compression stroke of the pump. This adversely affects the application or distribution of material from the spray gun applicator. The pressure spike problem is compounded if multiple guns are connected to a single manifold of a hot melt unit. Improved systems are needed which perform uniform and consistent material heating from reservoir to spray gun, and which create equal and constant pressures in each of the application devices. Improvements are also needed in the area of monitoring and controlling temperature and pressure for each application device.
The present invention provides an improved automated system for applying hot melt materials in a continuous manner, wherein hot melt material is uniformly heated and pressurized for controlled application to a substrate, and wherein pressure in each application device is individually monitored. In accordance with one aspect of the invention, there is provided a system for applying hot melt materials in liquid form wherein the materials to be applied must be heated, for example to within an approximate temperature range of 100xc2x0 F. to 400xc2x0 F. or greater (also referred to herein generally as xe2x80x9chigh temperaturexe2x80x9d) and pumped from a reservoir to an application device such as a spray gun. The system includes a hot melt unit having a material pump connected to a material reservoir. The hot melt unit has a manifold with an output connected to an application device such as one or more spray guns. The application device has a material passageway which leads to a nozzle, and a device manifold attached to the body of the application device. The device manifold has a material passageway connected to the material passageway of the application device and connected to an output from the hot melt unit. The device manifold has a sensor cavity, and a pressure sensor in the sensor cavity operative to sense pressure of material flowing through the device manifold and the application device. A heated recirculating manifold is connected to the hot melt unit and to the application device in such a manner that material pumped from the hot melt unit passes through the heated recirculating manifold prior to reaching the application device. The heated recirculating manifold has a manifold body with a material passageway, an entry port to the material passageway connected to an output of the hot melt unit, an exit port from the material passageway connected to the application device, a recirculating exit port for the material passageway connected to the hot melt unit, a heating element in thermal communication with the body of the manifold, a pressure regulator associated with the material passageway between the entry port and exit port, and a recirculation control valve associated with the material passageway and the recirculation exit port.